WASHINGTON (AP) -- Interest rates on short-term Treasury bills were unchanged in Monday's auction with rates on six-month bills remaining at their highest level since late March.

The Treasury Department auctioned $25 billion in three-month bills at a discount rate of 0.025 percent, the same as the last two weeks. Another $23 billion in six-month bills was auctioned at a discount rate of 0.050 percent, unchanged from last week.

The six-month rate is the highest since those bills averaged 0.065 percent on March 31.

The discount rates reflect that the bills sell for less than face value. For a $10,000 bill, the three-month price was $9,999.37 while a six-month bill sold for $9,997.47. That would equal an annualized rate of 0.025 percent for the three-month bills and 0.051 percent for the six-month bills.

Separately, the Federal Reserve said Monday that the average yield for one-year Treasury bills, a popular index for making changes in adjustable-rate mortgages, declined to 0.09 percent last week from 0.10 the previous week.